Ring oscillators include logic gates or analog amplifiers connected in a loop, that is, in a ring configuration. The output of one element is connected to an input of the next. An odd number of these components invert their input signal. Ring oscillators have many uses in electronics, and they can be used as entropy sources to generate true random numbers used in information security. However, at startup, ring oscillators rapidly change their internal temperatures, which together with circuit noise and environmental effects lead to multiple unpredictable oscillation frequencies. This uncertainty of startup behavior of ring oscillators makes the available entropy unpredictable, and therefore may harm the information security.
One existing solution to stabilize the startup behavior of a ring oscillator is to use a thermostat to stabilize the circuit temperature, which is expensive as this solution requires analog circuits. Another existing solution is to self-warm-up the ring oscillator, which does not ensure predictable startup conditions. A third existing solution is to use dummy circuits to generate heat before the ring oscillator starts, which is inaccurate and does not ensure predictable startup conditions.
Therefore it would be desirable to have a system and method that take into account at least some of the issues discussed above, as well as other possible issues.